Apparatus, system and method for high resolution identification with temperature dependent resistive device

ABSTRACT

A temperature measuring and identification (TMID) device obtains identification information and temperature information of a connected device having a temperature sensing circuit (TSC). The TSC includes a temperature sensing element (TSE) connected in parallel with a voltage clamping network (VCN) that limits the voltage across the TSE to an identification voltage within an identification voltage range when the voltage is greater than or equal to a lower voltage of the identification voltage range. When a voltage below the lower range is applied to the TSC, the VCN appears as an open circuit and the resistance of the TSC corresponds to temperature. A translation circuit within the TMID shifts TSC voltages within the identification voltage range to a normalization voltage range. Accordingly, voltages corresponding to temperature as well as voltages corresponding to identification are within the normalization voltage range. As a result, the resolution of a voltage sensing device used for measuring the temperature and identification voltages is maximized. In addition, the translation circuit maintains a minimal current during a rest state. For cost or other concerns, a first TSC may omit the VCN to provide a maximum identification voltage and other TSCs may include VCNs with lower identification voltage ranges.

TECHNICAL FIELD

The invention relates in general to temperature dependent resistivedevices and more specifically to an apparatus, system, and method forhigh resolution identification with temperature dependent resistivedevices.

BACKGROUND

Many systems and circuits utilize temperature sensing elements (TSEs) todetermine a temperature of a device. For example, typical temperaturedependent resistive devices (TDRD) such as thermistors may haveresistances that are inversely proportional to temperature. By measuringthe resistance of the thermistor, the temperature of the thermistor canbe determined. As a result, temperatures of components and devices nearthe thermistor can also be determined or estimated. Resistance sensingtechniques are sometimes used as identification techniques to determinethe identity of a device, module, or other peripheral unit that isconnected to a main device or main assembly. For example, portablecommunication devices that accept more than one type of modular batteryinclude a battery identification technique to determine the type ofbattery that is connected to the portable communication device. In orderto minimize components and contacts, conventional designs often combinetemperature sensing techniques and identification techniques. Forexample, some conventional portable communication devices that acceptmore than one type of modular battery include a temperature sensingmechanism that connects to circuits within the battery packs todetermine temperature and to identify the battery module. Each type ofbattery module includes thermistor circuits having differentcharacteristics allowing the portable communication device to identifythe particular battery module that is connected. Typically, eachthermistor circuit has a resistance to temperature relationship that isoffset from relationships of other thermistor circuits within othertypes of battery modules. Conventional systems are limited, however, inthat the resistance-to-temperature relationships of different circuitstypically overlap. FIG. 1, for example, is a graphical illustrationshowing two curves 102, 104 representing the resistance vs. temperaturerelationship for two conventional battery modules where the curvesoverlap. The overlap region 106 results in ambiguous data since ameasurement of a resistance within the overlap region is associated withboth of the curves 102, 104. The measurement may correspond to one typeof battery module at a low temperature or another type of battery moduleat a higher temperature. For example, resistance R may correspond to atemperature of T1 if one battery module is used and a temperature of T2if another battery is connected. This error could lead to catastrophicresults. A battery could explode where a battery module is inaccuratelyidentified and an incorrect charging scheme is applied. Further, thedynamic range and accuracy of the temperature measuring circuit isreduced as the number of identification devices is increased as well asrequiring a unique voltage-to-temperature transfer function for each ofthe possible curves. In addition, these problems are exacerbated as thenumber of IDs is increased.

Accordingly, there is a need for an apparatus, system and method forhigh resolution identification with temperature dependent resistivedevices.

SUMMARY

A temperature measuring and identification (TMID) device obtainsidentification information and temperature information of a connecteddevice having a temperature sensing circuit (TSC). The TSC includes atemperature sensing element (TSE) connected in parallel with a voltageclamping network (VCN) that limits the voltage across the TSE to anidentification voltage within an identification voltage range when thevoltage is greater than or equal to a lower voltage of theidentification voltage range. When a voltage below the lower range isapplied to the TSC, the VCN appears as an open circuit and theresistance of the TSC corresponds to temperature. A translation circuitwithin the TMID shifts TSC voltages within the identification voltagerange to a normalization voltage range. Accordingly, voltagescorresponding to temperature as well as voltages corresponding toidentification are within the normalization voltage range. As a result,the resolution of a voltage sensing device used for measuring thetemperature and identification voltages is maximized. In addition, thetranslation circuit maintains a minimal current during a rest state. Forcost or other concerns, a first TSC may omit the VCN to provide amaximum identification voltage and other TSCs may include VCNs withlower identification voltage ranges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical illustration of a resistance to temperaturerelationship of two conventional identification and temperature sensingcircuits.

FIG. 2A is a block diagram of a temperature sensing circuit (TSC)connected to a measuring temperature measuring and identification device(TMID device) in accordance with the exemplary embodiment.

FIG. 2B is a block diagram of a translation circuit in accordance withthe exemplary embodiment.

FIG. 3A is a graphical illustration of the voltage (V_(DP)) at thedetection port during measuring, diagnostic, and identificationprocedures in accordance with the exemplary embodiment.

FIG. 3B is a graphical illustration of the voltage (V_(DP)) and atranslated voltage range for a system having four identification valuesin accordance with the exemplary embodiment.

FIG. 4 is a schematic representation of an exemplary implementation ofthe temperature measuring and identification device (TMID device) wherethe translation circuit includes field effect transistors (FETs).

FIG. 5 is a graphical illustration of a relationship between thecurrents and voltages in a translation circuit in accordance with theexemplary embodiment.

FIG. 6 is a block diagram of a plurality of temperature sensing circuits(TSCs) of an identification system including four identification values(IDs) in accordance with the exemplary embodiment.

DETAILED DESCRIPTION

FIG. 2A is a block diagram of a temperature sensing circuit (TSC) 202connected to a temperature measuring and identification (TMID) device204 to form a temperature measuring and identification circuit 200. Asdiscussed in further detail below, the TSC 202 is one TSC of a set ofTSCs where the characteristics of the TSCs allow the TMID device 204 todistinguish between the different sets of TSCs. The TSCs can beinstalled within different devices providing a mechanism for monitoringthe temperature of a device and for identifying the device. An exampleof suitable application of the temperature measuring and identificationcircuit 200 includes installing a different TSC within each type ofbattery module accepted by a portable device. The TMID device 204 can beimplemented as part of portable device to identify different types ofbattery modules and to determine the temperature of the battery module.

Each TSC 202 includes at least a temperature sensing element (TSE) 208.At least one TSCs of a TSC set includes a voltage clamping network (VCN)206 connected in parallel to the TSE 208. In the exemplary embodiment, alinearization resistor (not shown in FIG. 2) is also connected inparallel to the TSE 208 in all of the TSCs in order linearize thetemperature to resistance curves of the TSC 202.

The TMID device 204 connects to the TSC 202 through a connectioninterface 210 that includes at least a detector port 212. The connectioninterface 210 may include any of numerous types of connectors, contacts,or electrical connection mechanisms to provide an electrical connectionbetween the TMID device 204 and the TSC 202. The exemplary connectioninterface 210 also includes a ground connector. Additional contacts maybe used for other signals in some circumstances.

As described below, each set of TSCs of the plurality of TSCs includes adifferent VCN where the VCN may include any combination of resistorsand/or voltage clamping devices, such as diodes. The VCN may be omittedfrom one set of TSCs to create an identification value (ID) that is notvoltage clamped. When the TSC is connected to the TMID device 204, thevoltage at the detection port 212 depends on the particular VCN 206, thetemperature, and the status of voltage source 214 in the TMID device204. The VCN limits the detector port voltage to a voltage within an IDvoltage range. The number of ID voltage ranges depends on the number ofTSC sets that can be connected to the TMID device 204.

The TMID device 204 includes a voltage supply 214 connected to thedetection port 210 through a translation circuit 216. A voltagereference scaler 218 scales the supply voltage to a voltage that is lessthan the supply voltage to provide a reference voltage to a voltagesensor 220. A controller 222 is configured to control the translationcircuit 216 and to receive a voltage measurement from the voltage sensor220. In response to a control signal, the translation circuit 216provides an identification voltage bias to the TSC 202 during a deviceidentification state and a temperature voltage bias during a temperaturemeasuring state. During the identification state, the translationcircuit 216 shifts the voltage at the TSC to the normalization voltagerange. Based on the voltage measurement and the status of the controlsignal, the controller 222 determines the temperature of the TSE 208 andan ID of the TSC 200 from a plurality of IDs. As discussed below, thevoltage sensor 220 and the controller 222 are implemented within aprocessor in the exemplary embodiment.

The TMID device 204 controls the voltage at the detection port (VDP) byswitching transistors within the translation circuit 216. During theidentification state, a sufficiently high current is applied to thedetection port to invoke the voltage clamping function of the VCN 206while a scaling network scales the clamped voltage to a correspondingvalue within the normalization voltage range. During the temperaturemeasuring state, the current into the detection port is sufficientlyreduced to prevent the voltage clamping function allowing the voltagesensor 218 to measure the resistance of the TSE which is used todetermine the temperature. In this temperature measuring state, thevoltage (V_(DP)) measured by the voltage sensor 220 at the detectionport 212 is processed by the controller 222 to determine the temperatureof the TSE 208 or to determine that an error condition exists. Where thedetected voltage is within a temperature measuring voltage range, thevoltage (V_(DP)) at the detection port corresponds to the resistance ofthe TSE 208 and the controller 222 calculates the temperature based onthe detected voltage. If the voltage is outside the range, thecontroller 222 determines that an error condition exists.

The voltage sensor 220 is an analog to digital converter (ADC) in theexemplary embodiment. The voltage reference scaler 218 provides areference voltage that is at or near the maximum value of thenormalization voltage range. Accordingly, the number of quantizationlevels of the ADC used for measuring voltage is increased. The increasedresolution improves the accuracy of the measurements. For example, ifthe supply voltage is equal to Vdd and the reference voltage to the ADCis Vdd/2, the normalization voltage range may be set to 0 to Vdd/2 andall of the quantization levels of the ADC are distributed between 0 andVdd/2. As compared to a system that does not shift the VDP voltage to anormalization voltage range, the ADC resolution and accuracy will bealmost double.

FIG. 2B is a block diagram of a translation circuit 216 in accordancewith the exemplary embodiment. Although the functional blocks shown inFIG. 2B may be implemented using any combination of firmware hardwareand/or software, the translation circuit 216 includes an arrangement oftransistors and resistors as well as other electrical components in theexemplary embodiment. The translation circuit 216 comprises an ID biascircuit 224, a temperature measuring bias circuit 226 and a scalingnetwork 228. During the identification state, the control signalactivates the ID bias circuit 224 and the temperature measuring biascircuit 226 to provide a sufficiently high voltage at the detection port212 to activate the VCN 206. As explained below in further detail, anetwork of transistors and resistors connected to the supply voltage 214establish a bias voltage as the detection port 212. The resultingvoltage (VDP) at the detection port depends on the particular VCN 206.The scaling network 228 scales the voltage to a corresponding valuewithin the normalization voltage range.

In the temperature measuring state, the control signal is changed to alevel that deactivates the ID bias circuit 224. The temperaturemeasuring bias circuit 226, however, remains active and provides avoltage that is less than the ID voltage range of the VCN 206. In theexemplary embodiment, a charge storage element, such as capacitor,maintains an appropriate control voltage at the temperature measuringbias circuit 226 for a time sufficiently long to allow a measurement ofthe detection port voltage. The scaling network is at least partiallyinactivated to maximize the dynamic range of the detection port voltage.

FIG. 3A is a graphical illustration of the voltage (V_(DP)) at thedetection port 212 during measuring, diagnostic, and identificationprocedures. FIG. 3B is a graphical illustration of the voltage (V_(VS))at the input 221 to the voltage sensor 220 and a relationship 334between the detection port voltage (V_(DP)) and the voltage sensor inputvoltage (V_(VS)). The various values and ranges depicted in FIG. 3A and3B are not necessarily to scale and are provided to generally illustraterelationships between different voltages and temperatures duringdifferent conditions. The graphical illustrations show an example of therelationship 334 between the detection port voltage and the voltage atthe input to the voltage sensor 220 where the translation circuit shiftsthe V_(DP) voltages to a normalization voltage range 303. In theinterest of brevity and clarity values shown in FIG. 3A and 3B may beapproximations of actual values observed in practice due tocharacteristics of the components of the TMID. For instance, theillustrated example indicates that the translation circuit does notshift the detection port voltages during the temperature measuring stateand the detection port voltage appears at the input of the voltagesensor 220. The actual voltage at the voltage sensor input 221, however,may vary from the detection port voltage as result of voltage drops dueto current flowing into the voltage sensor 220.

During the temperature measuring state, only the temperature measuringbias circuit is active and the voltage (V_(DP)) indicates a temperatureor an error condition. If the voltage (V_(DP)) is above an uppertemperature measuring voltage (V_(UTM)) 302 of the temperature measuringvoltage range (V_(MR)) 304, the voltage sensor 220 detects a voltage(V_(VS)) that is at maximum quantization level and the controller 222determines that no TSC 202 is connected to the TMID device 204. If thevoltage (V_(DP)) is at or near the supply voltage (Vdd) of the TMIDdevice 204, for example, the voltage indicates that no current isflowing through the detection port 212 and that no circuit is connectedto TMID device 204. The corresponding voltage (V_(VS)) at the voltagesensor input 221 is above the reference voltage (V_(REF)) 336 and theADC is “railed” high. If the voltage is below a lower temperaturemeasuring voltage (V_(TLM)) 308 of the temperature measuring voltagerange (V_(MR)) 304, the controller 222 determines that something otherthan a valid and properly operating TSC is connected to the TMID device204. For example, a voltage near zero can indicate a short circuiteddetection port 212 that may be due to a failed TSC or an invalid TSCdevice that is not intended to be connected to the TMID device 204. If,during the temperature measuring state, the voltage (V_(DP)) is withinthe temperature measuring voltage range (V_(MR)) 304, the voltage(V_(DP)) and the input voltage (V_(VS)) correspond to a temperature ofthe TSE 202 where the temperature may be measured between a minimumtemperature (T_(MIN)) 310 and a maximum temperature (T_(MAX)) 312. Inthe exemplary embodiment, where the TSE is an NTC thermistor, a maximumvoltage (V_(UTM)) corresponds to the minimum temperature (T_(MIN)). Therelationship between detector port voltage (V_(DP)) and temperaturefollows a temperature curve 301. The shape of the curve 301 depends onthe temperature sensing element (TSE) 208 characteristics as well asother components in the circuit. In the exemplary embodiment, alinearization resistor is connected in parallel with the TSE 208 inorder to make the curve 301 more linear as compared to a TSC thatincludes a TSE without a linearization resistor.

During the identification state, the detection port voltage (V_(DP))corresponds to an identification value (ID) of the TSC 202. The scalingnetwork 228 shifts the detection port voltage (V_(DP)) to within thenormalization voltage range 303. The voltage sensor input voltage(V_(VS)) corresponding to the detection port voltage indicates the ID ofthe TSC 202. In the exemplary embodiment, the scaling network 228slightly compresses the detection port ID voltage range. As explained infurther detail below, the scaling network includes a voltage divider inthe exemplary embodiment resulting in a non-zero minimum value of theshifted voltage sensor input voltage. A detection port voltage above theupper temperature measuring voltage (V_(UTM)) 302 is associated with oneof at least two ID voltages or ID voltage ranges. The number of voltageIDs depends on the number of TSCs in the set of TSCs that may beconnected to the TMID device 204. When both bias circuits 224, 226 areactive, the controller 222 determines the ID of the TSC 202 based on thevoltage (V_(VS)) at the voltage sensor that corresponds to the voltage(V_(DP)) at the detection port 212. The bias circuits 224, 226 andvoltage supply 214 are configured to provide a detection port voltageabove the upper temperature measuring voltage temperature (V_(UTM)) 302when the voltage source 214 is on. An example of a suitable schemeincludes having one TSC that does not include a VCN and that results ina first ID voltage (VID1) that is near the maximum voltage 306 and thatcorresponds to a first (ID1), a second TSC that includes a VCN thatlimits the voltage near V_(UTM) 302 to define a second ID (ID2), andadditional TCSs that include VCNs that result in ID voltage ranges thatare between the ID voltage (VID1) and the second ID voltage (VID2). Themaximum number of ID voltage ranges depends on the available voltagerange between the V_(UTM) and the maximum voltage 306 as well as thesize of the ID voltage ranges. The maximum voltage 306 is the voltagecorresponding to the minimum temperature since the thermistor has amaximum resistance at the minimum temperature. As explained below, thevarious components are selected such that the worst case maximum voltageof the thermistor is less than conduction voltage of the VCN that occursat the lowest operating temperature.

FIG. 3A and FIG. 3B illustrate an exemplary system that supports fourIDs although any combination and number of ID voltages may be used togroup TSCs into ID categories. A first ID voltage 306 results when afirst type TSC that does not include a VCN is connected to the TMIDdevice 204 and the voltage source 214 is on. A second ID voltage resultswithin a voltage range 314 when a second type TSC that includes a VCN isconnected to the TMID device 204 and the voltage source 214 is on. IDvoltages result within a third voltage range 316 and a fourth voltagerange 318 when a third type TSC and a fourth type TSC are connected tothe TMID device 204, respectively.

The translation circuit 216 shifts the ID voltage ranges of thedetection port to normalized ID voltage ranges at the voltage sensorinput 221. Therefore, each upper ID voltage 322, 326, 330 and each lowerID voltage 320, 324, 328 of each ID voltage range 314, 316, 318 areshifted to a corresponding lower normalized ID voltage 338, 340, 342 andupper normalized ID voltage 344, 346, 348 of corresponding normalized IDvoltage range 350, 352, 354, respectively. When the voltage sensor 220indicates a voltage (V_(VS)) at the input 221 that is within anormalized ID voltage range, the controller 222 determines that the TSCconnected to the TMID device has an ID corresponding to the normalizedID voltage range. Therefore, the controller 222 determines that the TSChas one of four IDs for the scheme illustrated in FIG. 3A and FIG. 3B.As discussed below, the IDs associated with an ID voltage rangecorrespond to the TSCs that include VCNs. Since the voltage clampingdevices within the VCN, such as diodes, have a forward voltage thresholdthat varies between devices and over temperature, the ID voltageresulting from a particular TSC may vary from a lower voltage to anupper voltage of the corresponding ID voltage range. Accordingly, thesecond ID voltage range 314 includes a lower voltage (VID_(L2)) 320 andan upper voltage (VID_(U2)) 322, the third ID voltage range 316 includesa lower voltage (VID_(L3)) 324 and an upper voltage (VID_(U3)) 326, andthe fourth ID voltage range 318 includes a lower voltage (VID_(L4)) 328and an upper voltage (VID_(U4)) 330.

FIG. 4 is a schematic representation of an exemplary implementation 400of the temperature measuring and identification circuit 100 where thevoltage sensor 220, and the controller 222 are implemented within aprocessor 402. The various components and functions described above withreference to FIG. 1 can be implemented using other combinations ofhardware, software, and/or firmware. In the exemplary implementation,the controller 222 controls a general purpose input/output (GPIO) port404 of the processor 402 to generate the control signal. The processor402 may be any type of general purpose processor, application specificintegrated circuit (ASIC), or other microprocessor or processorarrangement, that can perform the functions described herein. Coderunning on the processor 402 facilitates the functions of the controller222 as well as other functions of the TMID device 204. In the examplediscussed with reference to FIG. 4, the transistors are field effecttransistors (FETs). Other types of transistors or switching elements maybe used in some circumstances to perform the described functions.

The controller 222 controls the GPIO port 404 to place the GPIO port 404in an output (on) state and an off state. In the output state, the GPIOport 404 provides a voltage at or near the supply voltage (Vdd). In theoff state, the GPIO port 404 presents a voltage at or near ground (0V).As described below in further detail, the control signal, having avoltage (V_(CONT)) 406, activates transistors within the translationcircuit 216 to place the circuit 216 in a rest state or anidentification (ID) state. Circuit elements within the translationcircuit 216 enable a temperature measuring state during a time periodwhen the translation circuit 216 transitions from the ID state to therest state. An analog-to-digital converter (ADC) 408 measures thevoltage (V_(ADC)) at the output 410 of the translation circuit 216 byproviding the controller 222 with a digital representation of thevoltage (V_(ADC)). The elements of the TSC 202 form circuits with thetranslation circuit 216 where the detection port voltage (V_(DP))corresponds to the ADC-measured voltage (V_(ADC)) to allow a temperaturemeasurement in the temperature measuring state and an identificationvalue (ID) when the translation circuit 216 is in the ID state.

Any one of at least two TSCs 202 can be connected to the TMID device204. FIG. 4 illustrates a TSC 202 that includes a linearization resistor(R_(LIN)) 412, a TSE 208 and a VCN 206, where the TSE 208 is athermistor 208 and the VCN 206 includes an identification resistor(R_(ID)) 414 in series with a voltage clamping device 416. In theexemplary implementation, the voltage clamping device 416 is a diodearrangement 416 that includes one or more diodes that have a forwardvoltage within a forward voltage range. The voltage range depends on thenumber and type of diodes. For example, a typical PN junction, silicondiode has a forward voltage of approximately 0.7 volts. Two silicondiodes in series will have a collective forward voltage of about 1.4volts. Due to manufacturing variations and other factors, the forwardvoltage of a particular diode may be greater than or less than theexpected voltage drop. Further, the forward voltage varies overtemperature. Accordingly, a voltage range is defined for the diodearrangement 416 where any particular diode arrangement will have aforward voltage within the range. Examples of other suitable diodearrangements include arrangements using single Zener diodes and activeZener diodes. Zener diodes can be used with reverse bias to maintain afixed voltage across their terminals. In addition, the voltage clampingvariations of Zener diodes are typically less than the forward voltagevariations of PN junction silicon diodes over temperature, bias currentand manufacturing variations. Active Zener diodes may be preferred insome circumstances since active Zener diodes, also known as “shuntregulators” have variations in clamping voltages lower than normal Zenerdiodes.

During the rest state of the TMID 204, the GPIO port 404 is set to acontrol voltage (V_(CONT)) 406 at or near the supply voltage (Vdd). Inthe exemplary embodiment, the first field effect transistor (FET1) 418and the second field effect transistor (FET2) 420 are P channel FETs.Accordingly, when the GPIO port 404 is set to a logic level “high” nearVdd, the two FETs 418, 420 are off and no current flows through thetranslation circuit 216. Therefore, the rest state of the TMID 204provides a minimum current draw.

During the ID state, the GPIO port 404 is set to an off state where thevoltage at the GPIO port 404 is at, or near, zero volts. As a result ofthe low voltage at the gates of the FETs 418, 420, the first FET (FET1)418 and second FET (FET2) 420 are turned on. For this discussion, theresistances of FET1 418 and FET2 420 are considered to be much less thanthe resistances of a first resistor (R1) 422 and second resistor (R2)424. The second resistor (R2) 424 has resistance value such that if thefirst FET (FET1) 418 is off, voltage at the detection port 212 will notbe sufficient to activate the clamping function of the VCC 206. Theresistance value of the first resistor (R1) 422, however, is sufficientto activate the clamping function of the VCC 206. Accordingly, thevoltage (V_(DP)) at the detection port 212 is clamped at the ID voltageestablished by the VCC 206 when the GPIO port is at logic level low andthe FETs are on. In this state, the detection port voltage is shifted bythe translation circuit 216 to provide a normalized voltage at the ADC408. The voltage divider formed by the third resistor (R3) 426 andfourth resistor (R4) 428 reduces the ID voltage at the detection port212 to the normalized ID voltage at the ADC 408. When the first FET(FET1) 418 is on, current flows through the voltage divider formed bythe fifth resistor (R5) 430 and the sixth resistor (R6) 432. Theresulting voltage across the sixth resistor (R6) 432 is sufficient toturn on the a third FET (FET3) 434. As a result, the fourth resistor(R4) 428 forms the voltage divider with the third resistor (R3) 426. TheADC 408 converts the analog voltage measurement at the output 410 of thetranslation circuit 216 to a digital value that is processed by thecontroller 222 to determine the identification value of the TSC 202.

The GPIO port 404 is switched from low to high to perform a temperaturemeasurement. Immediately after the GPIO is switched to logic high, thevoltage at the gate of the first FET (FET1) 418 reaches a voltagesufficiently high to turn off the first FET (FET1) 418. A bias storagecircuit 435 keeps the gate of the second FET (FET2) 420 at a voltagesufficient to keep the second FET on, however. For the example, the biasstorage circuit 435 includes a diode 436, a capacitor 438 and a resistor440. Due to the diode 436 between the gate of the second FET (FET2) 420and the GPIO port 404, the second FET (FET2) 420 remains on for a timeperiod. The RC network formed by the capacitor 438 and a seventhresistor (R7) 440 keeps the second FET (FET2) 420 on until the capacitor438 discharges sufficiently to establish a gate-to-source voltage(V_(gs)) that is less than the threshold V_(gs) of the second FET (FET2)420. The second FET (FET2) 420 is turned off when the V_(gs) voltagedrops below the V_(gs) threshold. A temperature measurement is obtainedduring the time period when the first FET (FET1) 418 is off and thesecond FET (FET2) 420 is on. During this time period, the third FET(FET3) 434 is off and the fourth resistor (R4) 428 does not form avoltage divider with the third resistor (R3) 426. Accordingly, thevoltage (V_(DP)) at the detection port 212 is not scaled or shiftedduring the temperature measuring state to provide a voltage at the ADC404 that is essentially equal to the voltage (V_(DP)) at the detectionport 212. Since the second resistor (R2) 424 is selected such that thehighest possible voltage at the detection port 212 is half of the supplyvoltage (Vdd/2), the voltage at the ADC 404 ranges between 0 and Vdd/2.As discussed above, the voltage reference 218 is set to Vdd/2 allowingthe full resolution of the ADC 404 to be used for temperaturemeasurements.

The values of the components in the exemplary embodiment depend on theparticular implementation should and are in accordance with thefollowing general criteria.I ₂<I ₁;   (1)I _(ADC)<<I ₂;   (2)I _(ADC)<<I _(R3+R4);   (3)I _(R5+R6)<<I ₂;   (4)I _(R3+R4)<<I ₁+I ₂;   (5)I _(GFET3)@I ₂<V _(GSTHFET3)<Vdd; and  (6)I _(RTH)<<I ₁;   (7)

where I₁ is the current 442 through the first FET (FET1) 418, I₂ is thecurrent 444 through the second FET (FET2) 420, I_(ADC) is the current446 into the ADC 408, I_(R3+R4) is the current 448 through the fourthresistor (R4) 428; and I_(R5+R6) is the current 450 through the sixthresistor (R6) 432. The current flow in the translation circuit may bemodeled such that I₁ has a component current (I_(ID)) 452 that flowsthrough the VCC 206, a component current (I_(RTH)) that flows throughthe parallel combination of the thermistor 208 and linearizationresistor 412, a component current (I_(R5+R6)) 450 that flows through thesixth resistor (R6) 432 and a component current (I_(R3+R4)) that flowsthrough the fourth resistor (R4) 428.

FIG. 5 is a graphical illustration of a relationship 500 between thecurrents and voltages in the translation circuit 216. A first graph 502illustrates the control voltage 406 as the GPIO port is switched from alogic high to a logic low and back to the logic high. A second graph 504shows the current (I₁) 442 through the first FET 418. As illustrated,the current (I₁) 442 transitions from zero amps to the current (I_(ID))452 through the VCC 206 when the control voltage is switched to low. Athird graph 506 shows the current (I₂) 444 through the second FET 420transition from zero amps to the current (I_(RTH)) through thethermistor-resistor combination when the control voltage switches fromhigh to low. A fourth graph 508 shows the sum of the FET currents (I1and I2) transition from zero to the total current (I_(ID)+I_(RTH))through the TSC 202 when the control voltage is switched from high tolow. When the control voltage is switched to high, the current throughthe second FET continues to flow until the gate voltage of the secondFET drops blow the Vgs threshold (Vgsth(−)) of the second FET which isshown is the fifth graph 510. During this time period, the current inthe fourth graph is equal to the current through the thermistor andlinearization resistor combination and, therefore, indicates thetemperature of the TSC 202. The sixth graph 512 shows the voltage(V_(DP)) at the detection port 212 to be between Vdd/2 and Vdd when thecontrol voltage is low. During the temperature measuring state, theV_(DP) is between 0V and Vdd/2. The translation circuit 216 translatesthe V_(DP) to the V_(ADC) 410 shown in the seventh graph 514 where theID voltages range from Vdd/4 to Vdd/2 and the temperature voltages rangefrom 0 to Vdd/2.

FIG. 6 is a block diagram of a plurality of temperature sensing circuits(TSCs) 600 of an identification system including four identificationvalues (IDs) 602, 604, 606, 608. The TSCs of a first set of TSCs 610have a first identification value (ID1) 602, the TSCs of a second set ofTSCs 612 have a second identification value (ID2) 604, TSCs of a thirdset of TSCs 614 have a third identification value (ID3) 606, and theTSCs of a fourth set of TSCs 616 have a fourth identification value(ID4) 608. In the exemplary system, the TSCs of the first set 610include only a temperature sensing element 208 and a linearizationresistor 408 and do not include a VCN. Accordingly, ID1 corresponds tothe first voltage ID 306 shown in FIG. 3.

The TSCs of the second set 612 include a temperature sensing element208, a linearization resistor 412, and a VCN 414 that includes a voltageclamping device 416. The VCN 618 does not include an identificationresistor 410. Accordingly, the second ID corresponds to the second IDvoltage range 314.

The TSCs of the third set 614 include a temperature sensing element 208,a linearization resistor 408, and a VCN 620 that includes a voltageclamping device 416 and an identification resistor 414 having a first IDresistance 622. The third ID corresponds to the third ID voltage range316.

The TSCs of the fourth set 616 include a temperature sensing element208, a linearization resistor 412, and a VCN 624 that includes a voltageclamping device 416 and an identification resistor 414 having a secondID resistance 626. The fourth ID corresponds to the fourth ID voltagerange 318.

The values of the components of the TSC 202 and the TMID device 204 areselected based on the number of IDs, the desired temperature measuringrange, the supply voltage and other factors. Typically, the worst caseupper voltage limit corresponds to the minimum temperature of a negativetemperature coefficient (NTC) thermistor. Accordingly, the values of thecomponents are selected such that the worst case upper voltage limit isless than the lowest forward voltage limit of the voltage clampingdevice 416 (diode arrangement) which typically occurs at the highesttemperature due to the negative temperature coefficient of the diode.The maximum dynamic range for a temperature measurement can be achievedby using an appropriately low reference during the temperatureconversion.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. The above description is illustrative and not restrictive.This invention is to be limited only by the following claims, whichinclude all such embodiments and modifications when viewed inconjunction with the above specification and accompanying drawings. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

1. A temperature measuring and identification (TMID) device fordetermining an identification value and a temperature of anidentification device comprising a voltage clamping network in parallelwith a temperature sensing element, the voltage clamping networkconfigured to limit a voltage at a detection port to an identificationvoltage range when the voltage is greater than or equal to a lowervoltage of the identification voltage range, the TMID device comprising:a translation circuit, operatively coupled to the detection port,configured to shift the voltage to a normalized identification voltagewithin a temperature measuring voltage range during an identificationstate, the temperature measuring voltage range having an uppertemperature measuring voltage less than a clamped voltage resulting fromthe voltage clamping network limiting the voltage; and a controller,operatively coupled to the translation circuit, for determining theidentification value based on the normalized identification voltage. 2.The TMID device of claim 1, wherein the translation circuit is furtherconfigured to present, at the detection port during the identificationstate, an identification measuring voltage sufficiently high to invoke aclamping function of the voltage clamping network to produce the clampedvoltage at the detection port.
 3. The TMID device of claim 2, whereinthe translation circuit is further configured to present, at thedetection port during a temperature measuring state, a temperaturemeasuring voltage sufficiently low to avoid invoking the voltageclamping function.
 4. The TMID device of claim 2, wherein thetranslation circuit is configured to provide: the normalizedidentification voltage within a normalized voltage range at atranslation circuit output during an identification state, thenormalized identification voltage corresponding to the clamped voltageat the detection port; and a temperature measuring voltage within thenormalized voltage range at the translation circuit output, thetemperature measuring voltage resulting from a current flowing throughthe temperature sensing element during a temperature measuring state. 5.The TMID device of claim 4, further comprising: an analog to digitalconverter (ADC), operatively coupled to the translation circuit and tothe controller, configured to convert an output voltage at thetranslation circuit output to generate a digital identification voltageduring the identification state and to generate a digital temperaturemeasuring voltage during the temperature measuring state, wherein thecontroller is configured to determine an identification value of theidentification device based on the digital identification voltage and todetermine the temperature of the identification device based on thedigital temperature measuring voltage.
 6. The TMID device of claim 5,wherein the detection port is configured to connect to any one of aplurality of identification devices, each identification devicecomprising a voltage clamping network in parallel with a temperaturesensing element.
 7. The TMID device of claim 6, wherein when theidentification device is connected to the detection port, thetranslation circuit is further configured to: present, at the detectionport and in response to a first control signal level, an identificationmeasuring voltage sufficiently high to invoke a clamping function of theclamping circuit to produce the clamped voltage at the detection port;present, at the detection port and in response to a second controlsignal level, a temperature measuring voltage sufficiently low to avoidinvoking the voltage clamping function, present, at the translationcircuit output and in response to the first control signal level, thenormalized identification voltage corresponding to the clamped voltageat the detection port and within the normalized voltage range; andpresent, at the translation circuit output and in response to the secondcontrol signal level, the temperature measuring voltage within thenormalized voltage range and corresponding to the temperature of theidentification device.
 8. The TMID device of claim 7, furthercomprising: a first transistor, operatively coupled to a voltageterminal of the TMID device, configured to provide a first currentthrough the identification device in response to the first controlsignal level and to provide no current in response to the second controlsignal level; a second transistor, operatively coupled to the voltageterminal of the TMID device, configured to provide a second currentthrough the identification device in response to a first control signallevel; and a bias storage circuit, operatively coupled to the secondtransistor, configured to maintain a second transistor bias voltage fora time period after a control signal changes from the first controlsignal level to the second control signal level to allow the secondtransistor to provide the second current during the time period.
 9. TheTMID device of claim 8, further comprising: two resistors; a thirdtransistor configured to form a voltage divider with the two resistorsin response to the first control signal level, the voltage dividerconfigured to scale the clamped voltage to the normalized voltage,wherein the voltage divider is operatively coupled to the ADC.
 10. TheTMID device of claim 8, further comprising: a first resistor connectedbetween a source of the first transistor and the detection port, whereina gate of the first transistor is configured to receive the controlsignal; and a second resistor connected between a source of the secondtransistor and the detection port, wherein a gate of second transistoris connected to the bias storage circuit.
 11. The TMID device of claim10, wherein the bias storage circuit comprises: a capacitor connectedbetween a gate of the second transistor and a voltage supply; and adiode connected between the gate of the second transistor and the gateof the first transistor.
 12. The TMID device of claim 8, furthercomprising a general purpose input/output (GPIO) port, operativelycoupled to the controller, configured to generate the control signal inresponse to the controller.
 13. The TMID device of claim 5, where areference value for the ADC is less than the clamped voltage.
 14. TheTMID device of claim 13, wherein the reference value is equal to theupper value of the normalized voltage range.
 15. The TMID device ofclaim 4, wherein the clamped voltage is greater than the temperaturemeasuring voltage and greater than a maximum level of the normalizedvoltage range.